The present invention relates generally to generators that have a programmable output, and in particular to generators that employ digital sampling techniques to control a programmable output.
Generators that provide a programmable output having pulse capability generally employ either an analog control loop or a high-speed digital control loop in order to provide fast rise and fall times. When controlling the output pulse of a generator using digital sampling techniques the response time is largely a function of the sample rate and the group delays of the analog to digital (A/D) and digital to analog (D/A) converters. Therefore, a lower limit is placed on the response time of a digitally sampled control loop. Conventional digital control loops have been unable to provide response times that are not limited by the sample rates of the A/D and D/A that are used in the circuit. In addition, using a very fast A/D and DSP having a sufficient sample rate is expensive and requires additional circuit area.
While conventional generator control techniques can be used to provide programmable outputs having pulse capability, those techniques have not proven capable of extending the operational range of digital sampling control loops. Also, conventional generator control circuits require expensive high performance digital or analog techniques to be capable of providing pulse outputs with fast transition times.
The present control circuit and method extends the operating range of digitally sampled control loops without resorting to expensive A/D converters by controlling the programmable output of a generator. In particular, the output of the loop controller is driven to a predicted drive point which forces the programmable output to approximately the desired set point.
As subsequently described in greater detail, the programmable output includes an output level having a corresponding set point. The generator has a drive input that is driven to an actual drive point for controlling the output level of the programmable output. A set point corresponding to a requested output level is determined. A predicted drive point is then determined. The actual drive point of the generator drive input is forced to the predicted drive point. The output level of the programmable output is then sensed. A digital output signal that is representative of the sensed output level is generated. The actual drive point of the generator drive input is controlled based on the digital output signal, such that the output level of the programmable output is controlled. The actual drive point corresponding to the requested output level is then stored.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.